Stabilized macromolecular polyacetals and process for making the same

ABSTRACT

Improved stabilization of polyacetals against thermal and oxidative degradation, particularly stabilization of homopolymers of formaldehyde or its cyclic oligomers and of copolymers of trioxane with cyclic ethers or cyclic acetals is obtained by using a stabilizing agent which is a homopolymer of a poly-Nvinyl-azetidinone or a copolymer of an N-vinyl-azetidione and a minor amount of an olefinically unsaturated comonomer or mixtures of such homopolymers and copolymers. The stabilizing agents may be used in an amount of 0.05 to 10 percent by weight. Further improvement in stabilization is achieved by using the poly-Nvinyl-azetidinone stabilizing agents in combination with conventional phenolic stabilizers in that a synergistic effect between the two types of stabilizers is obtained.

United States Patent Inventors Appl. No.

Priorities Ernst Wolters;

Michael Lederer, both of Frankfurt am Main, Germany Feb. 17, 1970 Dec.7, 1971 Farbwerke Hoechst Aktiengesellschaft vormals Meister Lucius &Bruning Frankfurt am Main, Germany May I7, 1966 Germany Nov. 25, 1966,Germany, No. F 50761 Continuation-impart of application Ser. No.634,487, Apr. 28, 1967, now Patent No. 3,53 1 ,45 1, Continuation-impartof application Ser. No. 679,517, Oct. 31, 1967, now abandoned. Thisapplication Feb. 17, 1970, Ser. No. 12,144

STABILIZED MACROMOLECULAR POLYACETALS AND PROCESS FOR MAKING THE SAME 10Claims, No Drawings US. Cl

Primary Examiner-Murray Tillman Assistanl ExaminerC. J. SeccuroAttorney-Curtis, Morris and Safford ABSTRACT: Improved stabilization ofpolyacetals against thermal and oxidative degradation, particularlystabilization of homopolymers of formaldehyde or its cyclic oligomersand of copolymers of trioxane with cyclic ethers or cyclic acetals isobtained by using a stabilizing agent which is a homopolymer of apoly'N-vinyl-azetidinone or a copolymer of an N-vinylazetidione and aminor amount of an olefinically unsaturated comonomer or mixtures ofsuch homopolymers and copolymcrs. The stabilizing agents may be used inan amount of 0.05 to 10 percent by weight. Furtlher improvement instabilization is achieved by using the poly-N-vinyl-azetidinonestabilizing agents in combination with conventional phenolic stabilizersin that a synergistic effect between the two types of stabilizers isobtained.

STABILIZED MACROMOLECULAR POLYACETALS AND PROCESS FOR MAKING THE SAMEThis application is a continuation-in-part of U.S. application Ser. No.634,487 filed Apr. 28, 2967 now U.S. Pat. No. 3,531,451 and of U.S.application Ser. No. 679,517 filed Oct. 31, I967 now abandoned. Theclaims of this application are directed to the stabilized polyacetalsand method of making the same disclosed in application Ser. No. 679,517.

The present invention relates to the stabilization of macromolecularpolyacetals. Processes are already known for making macromolecularpolyacetals by polymerizing monomeric formaldehyde or oligomers offormaldehyde, for example, trioxane, in the presence of variouscatalysts. The polymers so obtained contain unstable terminal hydroxylgroups and are completely depolymerized within a short time withreformation of monomeric formaldehyde on being heated to a temperatureabove their melting point. This degradation reaction can be prevented toa certain extent by blocking the terminal groups.

Copolymers of formaldehyde or of oligomers of femaldehyde with cyclicacetals and cyclic ethers are also known. They contain ether bonds inaddition to acetal bonds in the polymer chain so that products which aremore heat resistant are obtained.

However, both the homopolyacetals containing stabilized terminal groupsand the copolymers containing some stable ether bonds in the chain aremore or less unstable under the action of heat produced, for example,when the products are processed on the usual processing machines. It hastherefore been proposed to mix the polymers with various stabilizers,for example, phenols, amines, hydrazines, ureas, thioureas andpolyamides. The stabilizing action of these substances is due to theircapacity to intercept the aldehydes formed in the thermal cleavage andtheir secondary products, to block the active centers occurring in thepolymer and thus to prevent depolymerization. Their effectivenessdifi'ers widely. Hydrazine-, ureaor thiourea-derivatives have anunsatisfactory stabilizing action as regards heat and oxygen. Phenolsand amines give rise to discoloration of the polyacetals and in manycases diffuse out of the polymer or can be removed therefrom bysolvents.

In view of these drawbacks of the aforesaid substances, polymericstabilizers which are generally difficulty volatile and cannot beremoved from the polyacetals by the usual solvents are of particularinterest. Thus it has been proposed to stabilize macromolecularpolyacetals using polymers of N- vinyl lactams of the general formula:

CHFCH-N :0

EZH!) n have a considerably improved stabilizing action against thermaland oxidative degradation of polyacetals as compared with the knownpoly-N-vinyl lactams and impart an improved resistance to ageing tomacromolecular polyacetals.

In the above formula R1 to R4 may be the same or different and may behydrogen atoms, aliphatic radicals with one to 12 carbon atoms,alicyclic and/or aromatic radicals. The aliphatic radicals may bestraight-chained or branched. Representative radicals are: CH C I-I n-CH n-C H,,, n- C6H131 1 is, s m e im IO ZIr u u c,,H,,, i-C H- i-C,Hsec.-C,H,,, i-C l-i i-C,H, i-C H i- C l l i-C l-l i-C I-I i-C H i-C Il-laliphatic 5- or 6- membered rings such as cyclopentyl or cyclohexyl, anunsubstituted phenyl radical or a substituted phenyl radical, such asthe p-tolyl, xylyl, methoxy phenyl, chlorophenyl and fluorophenylradicals. R, to R, are preferably alkyl groups of 7 one to four carbonatoms.

The structure of the above poly-N-vinyl-azetidinones differs from thatof the known poly-N-vinyl lactams in that which is bound to the polymerchain via the nitrogen atom as a side group, is smaller than 3 and thatthe hydrogen atoms in the ring may be replaced wholly or partially byaliphatic, alicyclic and/or aromatic radicals.

The stabilization of the polyacetals may also be carried out usingcopolymers of Nvinyl-azetidinones with a minor amount of anethylenically unsaturated comonomer such as acrylic and methacrylic acidesters of alkanols having one to 12 carbon atoms, vinyl esters ofcarboxylic acids having one to l9 carbon atoms, substituted orunsubstituted acrylamides, N- vinyl lactams with 5 to 7 members in thering and/or N-vinyl amides.

Examples of azetidinone polymers suitable for use according to thepresent invention are poly-N-vinyl-4-methylazetidinone,poly-N-vinyl-4,4-dimethyl-azetidinone, poly-N-vinyl-3,4-dimethyl-azetidinone, poly-N-vinyl-4-phenylazetidinone andcopolymers of N-vinyl-4,4-dimethylazetidinone andN-vinyl-N-methyl-formamide in a ratio of 85:15 to 68:32 parts by weight,respectively. The polymers and copolymers used as stabilizing agents inaccordance with the invention may be added in an amount within the rangeof 0.05 to 10 percent by weight, advantageously 0.1 to 2 percent byweight, based on the weight of the macromolecular polyacetal.

The efiectiveness of the stabilizers in accordance with the inventionmay be further considerably enhanced by the addition of 0.01 to 10percent by weight, advantageously 0.1 to 5 percent by weight, based onthe weight of the polyacetal, of a known antioxidant, e.g., a phenolicantioxidant such as phenol or a substituted phenol. Particularlyeffective are bisphenols, for example,2,2-methylene-bis-(4-methyl-6-tert. butylphenol) and4,4'-butylidene-bis-(6-tert. butyl3-methylphenol). When the stabilizersof the invention are used in combination with these antioxidants, a.pronounced synergistic effect is obtained. A small amount of thesesubstances is therefore sufficient to obtain a satisfactory stabilizingeffect. By the addition of known light stabilizers, for example,benzophenone-, acetophenone or triazine-derivatives, the properties ofthe polyacetals stabilized by the process of the invention may be stillfurther improved to obtain products of high utilitarian value.

The polymers of N-vinyl-azetidinone derivatives are easy to manufactureand to use. By polymerization of monomeric N- vinyl-azetidinones in aninert solvent, they are obtained, for example, in the form of a finepowder and may be incorporated in that form into the polyacetal with thehelp of a commercial mixer. lt is also possible to mix a solution of thestabilizer in an appropriate solvent with the polyacetal, whilestirring, and then to evaporate the solvent.

To illustrate the manner in which the N-vinyl-azetidinone homopolymersand copolymers used in the present compositions may be prepared, thefollowing examples of their preparation are given:

EXAMPLE A l0 Grams of N-vinyl-4,4-dimethylazetidinone were polymerizedin bulk with 0.1 gram of azo-bis-isobutyric acid nitrile as a catalystat about C. After 8 hours, a solid colorless polymer was obtained. Afterdissolution and reprecipitation from chloroform/ether, there wereobtained 5.5 grams of a polymer having a reduced specific viscosity of0.86. The turbidity point of the percent aqueous solution was at 39.4 C.

EXAMPLE B Grams of N-vinyl-4,4-dimethylazetidinone and 10 grams of vinylacetate were polymerized in bulk with 0.1 gram of azo-bis-isobutryricacid nitrile at 80 C. After a period of 8 hours, the colorless copolymerobtained was dissolved in chloroform and precipitated with diethylether. There were obtained 10.2 grams of a copolymer having a nitrogencontent of 7.5 percent corresponding to 67 percent by weight ofbetalactam which had been incorporated by polymerization. The reducedspecific viscosity of the copolymer was 0.33.

EXAMPLE C 8 Grams of N-vinyl-3,4-dimethylazetidinone and 2 grams ofmethylacrylate were polymerized in bulk with 0.05 grams ofazo-bis-isobutyric acid nitrile as the catalyst at 80 C. for 7 hours.The colorless copolymer obtained was dissolved in chloroform andreprecipitated with diethyl ether. There were obtained 5 grams of acopolymer having a nitrogen content of 7.2 percent. The reduced specificviscosity was 1.05.

EXAMPLE D 10 Grams of N-vinyl-3,4-dimethyl-azetidinone was polymerizedin 10 grams of methanol with 0.05 gram of azobis-isobutyric acid esterat 80 C. under exclusion of air. The polymer was then'isolated byprecipitation with diethyl ether and dried at 70 C. in vacuo. The yieldof polymer was 9.1 grams and it had a reduced specific viscosity of0.53.

EXAMPLE E 10 Grams of N-viny1-4-phenyl-azetidinone was polymerized in 50grams of benzene with 0.05 gram of azo-bis-isobutyric acid ester at 80C. and under the exclusion of air. The polymer was then isolated byprecipitation with diethyl ether and dried at 70 C. in vacuo. A yield-of2 grams of polymer was obtained having a reduced specific viscosity of0.041 measured in chlorofonn.

EXAMPLE F In a reaction vessel provided with a stirrer, a refluxcondenser, a thermometer and a dropping funnel, 680 cc. of water and 0.8cc. of a 25 percent -ND -water were heated to a temperature of 85 C.Under an atmosphere of N 160 grams of N-vinyl-4-methyl-azetidinonecontaining 0.4 gram of azo-bisisobutyric acid nitrile, were addeddropwise over a period of 30 minutes, while stirring. After apolymerization period of 8 hours, the aqueous solution of the polymerstill contained 0.2 percent by weight of residual monomer, correspondingto a conversion rate of 99 percent. The reduced specific viscosity ofthe product dissolved and reprecipitated from a mixture of CHCl; andether, was 1.08. The surface tension of the 1 percent solution in waterwas 61.3 dyn/cm. (at 20 C.).

EXAMPLE G In an apparatus as described in example F, 50 grams of N-vinyl-4,4-dimethylazetidinone were polymerized in 600 cc. of gasoline(boiling point 80-1 10 C.) with 0.5 grams of azo-bisisobutyric acidnitrile as the catalyst at a temperature in the range of from 87 to 90C. There were obtained 37 grams of a polymer having a reduced specificviscosity of 0.17. The turbidity point of a 5 percent aqueous solutionwas at 36 C. The surface tension of a 1 percent aqueous solution was48.7 dyn/cm. (at 20 C.).

EXAMPLE H In an apparatus as described in example F, 324 cc. of gasolinehaving a boiling point in the range of from 80 to 1 10 C. were heated toa temperature of about 90 C. 1n the 10.55 percent of nitrogen(determined by Dumas). By decomposing the copolymer with HCl, 1.3percent of nitrogen was obtained since only dimethylamine-nitrogen wasascertained by this method. The copolymer separated from its'turbid 5percent aqueous solution at 4546 C.

EXAMPLE .1

In an apparatus as described in example F, 324 cc. of gasoline having aboiling point in the range of from to 1 10 C. were heated to atemperature of about C. A solution of 128.56 grams ofN-vinyl-4-methylazetidinone, 32.14 grams of maleic acid bis-2-ethylhexylester, 0.5 gram of azo-bis-isobutyric acid nitrile and 162 cc. ofgasoline was added thereto, while stirring, over a period of 45 minutes.The copolymer separated as a powder and, after a period of 4 hours, 150grams of a copolymer having a reduced specific viscosity of 1.59 wasobtained. The composition was calculated from the nitrogen content of10.6 percent (by Dumas), which indicated 84 percent by weight ofN-vinyl4methy1azetidinone and 16 percent by weight of maleinate.

1n the foregoing examples A to D and F to J the reduced specificviscosities were measured at 20 C. using a 1 percent by weight solutionof the polymer in methanol. It will be noted that the viscosities of thepolymers fall within the range 0.1 5 to 1.6, thus indicating anapproximate molecular weight range of 30,000 to 300,000. While polymershaving molecular weights outside this range can be used as stabilizingagents in accordance with the present invention, those having molecularweights within this range are preferred. Monomer N-vinylazetidinones areprepared by cleavage of corresponding N-(aalkoxyethyl)-azetidinones inthe presence of acid catalysts at temperatures of from 50 to 300 C. TheN-(a-alkoxyethyl)- azetidinones are obtained by reaction ofazetidinones-(2) with acetals or semiacetals of acetaldehyde in thepresence of acid catalysts at temperatures of from 10 to 200 C.

To illustrate the manner in which the monomer N-vinylazetidinones may beprepared, the following examples are given:

EXAMPLE K a. A mixture of 495.5 grams of 4,4-dimethylazetidinone- (2),1046 grams of acetaldehyde diisobutyl acetal, 37 grams of isobutanol,grams of acetaldehyd and 2,5 grams of iron (11]) chloride was refluxedfor 4 hours at 70 to 80 C. After cooling the mixture was neutralizedwith a 30 percent aqueous solution of potassium hydroxide and fractionaldistilled. There were obtained 438 grams of N-(a-isobutoxy-ethyl)-4,4-dimethylazetidinone-(2) boiling at 114 C. under 8 torr and having arefractive index n of 1.4453. b. in a four-necked flask provided withstirrer, sump thermometer, nitrogen inlet tube, distilling column anddropping funnel, 50 grams ofN-(aisobutoxyethyl)-4,4-dimethyl-azetidinone-(2), in which 50 milligramsof H PO had been dissolved, were heated at C. under a pressure of 40torr, whereby cleavage occurred. In the same measure as the cleavageproducts distilled off, further 149 grams of N-(a-iso-butoxyethyl)-4,4-dimethylazetidinone-(Z), containing 1 percent ofH PO were dropped in. The sump temperature was maintained at to C., thetemperature at the head being kept at 110 C. by regulation of the refluxratio. In this manner only small amounts of starting material which hadnot undergone cleavage distilled off. After distillation of the reactionmixture there were obtained 90 grams of pureN-vinyl-4,4-dimethylazetidinone-(2) boiling at 79 C. under 12.5 torr.

EXAMPLE L a. Corresponding to example K and starting from 851 grams of4-methylazetidinone-(2), 310 grams of acetaldehyd, 1743 grams ofacetaldehyde diisobutyl acetal and 6 grams of anhydrous iron(lll)chloride there are obtained 1520 grams ofN-(a-iso-butoxyethyl)-4-methylazetidinone-(2) boiling at 107 C. under 8torr and having a refractive index n of 1.4432.

b. in a four-necked flask equipped as described in example K b 150 gramsof N-(a-isobutoxyethyl)-4-methylazetidinone- (2) and 75 grams of acidaluminum oxide were heated in a nitrogen atmosphere while stirring undera pressure of 90 torr. Cleavage set in at 135 C. The procedure wascontinued as described in example K b while maintaining a boiling limitof 1 10 C. During the course of 7 hours 770 grams ofN-(a-isobutoxy-ethyl)-4-methylazetidinone-(2) had undergone cleavage.When the cleavage products were distilled, 400 grams of pureN-vinyl-4-methyl-azetidinone-(Z) boiling at 71 to 72 C. under 9 torrwere obtained. The yield corresponded to 87 percent of the theory.

EXAMPLE M a. A mixture of 73.5 grams of 4-phenylazetidinone-(2), 261.5grams of acetaldehyde diisobutyl acetal, 0.2 gram of anhydrousiron(lll)chloride and 13 grams of acetaldehyde was heated slowly at 65C. and then maintained at this temperature for 3 hours. After coolingthe mixture was neutralized with a 30 percent solution of sodiumhydroxide in isobutanol and distilled. At a temperature of 99 to 105under a pressure of 0.05 torr there were obtained 100 grams ofN-(a-isobutoxyethyl)-4-phenyl-azetidinone-(2) having a refractive indexn of 1.5084. After some time the colorless viscous oil crystallized andthen had a melting point of 63 to 64 C. of 15 centimeters and containingspirals, 99 grams of N-(a-isobutoxyethyl)-4-phenyl-azetidinone-( 2) and5 grams of acid aluminum oxide were heated under a pressure of 0.2 torr.Cleavage took place at 155 to l60 C. and was terminated after 45minutes. The separated isobutanol was condensed in a cooling trap. Thevinyl compound was then separated from the aluminum oxide bydistillation. By fractionating distillation 48.5 grams of pureN-vinyl-4-phenyl-azetidinone-(2) boiling at 100 to 101 C. under 0.2 torrwere obtained. The conversion was 77.5 percent and the yield was 90percent of the theory.

The stabilizers in accordance with the invention are excellentlycompatible with the polyacetals and do not influence the mechanical andtechnological properties of the polymers. They have the particularadvantage that, contrary to most stabilizers of low molecular weight,they do not diffuse out of the polymer and cannot be removed therefromby the usual solvents. Owing to this fact, the stability of productsthat have been stabilized with these substances is preserved even aftera prolonged exposure to elevated temperatures and after contact withsolvents.

The stabilizers of the invention are colorless and prevent discolorationof the polymers thus stabilized, even when the latter are exposed for aprolonged time to heat, light and oxygen. Finally, the substances inaccordance with the invention provide excellent protection ofmacromolecular polyacetals against thermal oxidative depolymerizationand improve their resistance to ageing and are in this respectconsiderably superior to poly-N-vinyl lactams of similar structure with3 to 7 CH, groups in the ring.

The term macromolecular polyacetals" is used herein to mean:

1. homopolymers of formaldehyde or its cyclic oligomers, for example,trioxane, in which the terminal hydroxyl groups have been blocked byesterification or etherification, and (2) copolymers of trioxane andcyclic ethers or cyclic acetals which contain oxyalkylene groups with atleast 2, advantageously 2 to 4, neighboring carbon atoms in the mainpolymer chain. The amount of oxyalkylene groups may be within the rangeof 0.1 to percent by weight, advantageously 0.1 to 15 percent by weight,based on the total polymer weight. Such copolymers can be easilyobtained in known manner, for example, by cationic copolymerization oftrioxane with cyclic ethers and/or cyclic acetals. Comonomers that areparticularly suitable for the manufacture of the polymers are ethyleneoxide and its derivatives, oxacyclobutane, and cyclic forrnals, forexample, of glycols such as 1,3- or 1,4-butanediol, diethylene glycol or1 ,4butenediol.

To determine the stability of the polyacetals against heat andoxidation, the loss in weight of a granular sample in 30 minutes at 230C. under oxygen was measured. The resistance to ageing was determined oncompressed plates 0.5 mm. thick by annealing at 120 C. in a circulatingair drier.

The following examples serve to illustrate compositions embodying theinvention and methods of making such compositions, but are not intendedto limit the scope of the invention. in the examples parts are given byweight.

In the tables given in the examples, the test results ascertained withthe stabilizers of the invention have been com pared with those obtainedin test samples stabilized with the known poly-N-vinyl lactams having atleast 5 ring atoms. The tests were carried out with polyacetals whichhad a solution viscosity of 0.3 to 3 dl/g, advantageously 0.5 to 2 dl/g,determined in a 0.5 percent solution of the polymer in butyrolactonewith the addition of 2 percent diphenylamine as a stabillzer.

EXAMPLE 1 100 parts of an acetal copolymer of 98 parts of trioxane andtwo parts of ethylene oxide were intimately mixed in an impeller withtwo, five and eight pans, respectively, of the compounds indicated inthe following table I and granulated on a commercial extruder. After thegranular product had been dried for 2 hours at 100 C. in a vacuum drier,the stability was measured by determination of the loss in weight of agranular sample in 30 minutes at 230 C. in air.

The granular product was furthermore made into compressed plates 0.5 mm.thick and the resistance to ageing at elevated temperatures wasdetermined by annealing at 120 C. in a warming cabinet.

TABLE 1 Embrlttlement at 120 C. in warming cabinet in days Percentageloss in weight at 230 C. in

30 min. in air Amount in percent by Stabilizer Weight Without stabilizer(comparison) Poly-N-vinylyrrolidone (comparison 2 Poly-N-vinylcaprolactarn (comparison) 2 Poly-N-vinyi-4-methylazetidinone 2PolyN-vinyl-3,4-dimethylazetldinone Poly-N-vinyl-4-methylazetidlnonePo1y-N-vinyl-3,4-dimethylazotidinone 1 Completely brittle after 1 day.

www w wv- EXAMPLE 2 TABLE 2 Percentage loss in Embrittlement weight atat 120 C. in Amount Amount 230 C. in warming in percent in percent 30min. cabinet Stabilizer by weight Costebilizer by weight in oxygen indays Poly-N-vinylpyrrolidone 0. 1 2,2-methylene-bis(4-methy1-6-tert.butylphenol)... 0. 5 3. 2 1 Do- 0.3 do 0.5 3.4 1 8'2 5'2 i Pol -N-vinlea rolactam.

iI)o 0.6 4.1 1 D0. 0. 5 3. 6 1 Poly-N-vinyM-methylazetidinone- 0. 5 2. 48 Do. 0. 5 1. 9 7 D0. 0. 5 1. 8 7 Poly-N-vinyl-3,4-di1nethylazetldinone.0. 6 2. 2 7 o. 0. 5 2. D0- 0. 6 2.0 4

EXAMPLE 3 A copolymer of trioxane and 4 percent by weight of 1,3-dioxolane was intimately mixed with 0.7 percent by weight of4,4'-butylidene-bis-(6tert. butyl-3-methyl-phenol) and 0.2 percent byweight of one of the stabilizers indicated in the following table 3.After granulating, the loss in weight of the test samples was determinedafter heating for 30 minutes at 230 C. in air. Table 3 shows that thestabilizers in accordance with the invention are superior to thestabilizers used for comparison.

TABLE 3 Percentage loss in weight at 230 C.

Stabilizer after 30 minutes in air poly-N-vinyl'pyrro-idone (comparison)6.8

poly-N-vinyl-4-methylazetidinone. 3.2

poly-N-vinyl-3,4-dimethylazetidinone 4.1

EXAMPLE 4 An acetylated homopolymer of formaldehyde which had beenstabilized with 0.7 percent by weight of 2,2-methylenebis-(4-methyl-6-tert. butyl-phenol) and 0.3 percent by weightof poly-N-vinyl-3,4-dimethyl-azetidinone was made into compressed plateswhich were stored at 120 C. in a circulating air drier. Almost nodiscoloration was observed. Nor did a test sample which had beenstabilized in the same manner and heated for 30 minutes at 230 C. in aclosed mold undergo any discoloration. The loss in weight of thepolymers containing the above stabilizer combination was 2.8 percentafter 30 minutes at 230 C. in air.

The macromolecular polyacetals stabilized by the process of theinvention may advantageously be used for the manufacture of variouskinds of thermoplastic molding masses, for example, films, sheets,plates, ribbons and containers. They can be processed according to theusual methods, for example, by extrusion and injection molding.

We claim:

1. A process for stabilizing macromolecular polyacetals against thesimultaneous action of heat and oxygen, said polyacetal being ahomopolymer of formaldehyde or its cyclic oligomers or a copolymer oftrioxane and cyclic ethers or cyclic acetals, which copolymer containsoxyalkylene groups with at least two adjacent carbon atoms in the mainolymer chain, said process comprising incorporating in the po yacetal inwhich R to R each represents a hydrogen atom, a straight chained orbranched aliphatic radical with one to 12 carbon atoms, an alicyclic oraromatic radical, (2) copolymers comprising a major amount of saidN-vinyl-azetidinone and (3) mixtures of said homopolymers and saidcopolymers.

2. A process according to claim 1 wherein a mixture of saidnitrogen-containing polymer with another antioxidant or light stabilizeror with a mixture of another antioxidant and light stabilizer isincorporated in said polyacetal.

3. A thermoplastic, moldable polyacetal which is a macromolecularhomopolymer or formaldehyde or its cyclic oligomers or a copolymer oftrioxane and cyclic ethers or cyclic acetals, which copolymer containsoxalkylene groups with at least two adjacent carbon atoms in the mainpolymer chain, said polyacetal having incorporated therein as a anitrogen containing polymer selected from the group consisting of l)homopolymers of a N-vinyl-azetidinone of the formula in which R to Reach represents a hydrogen atom, a straight chained or branchedaliphatic radical with one to 22 carbon atoms, an alicyclic or aromaticradical, (2) copolymers comprising a major amount of saidN-vinyl-azetidinone and (3) mixtures of said homopolymers and saidcopolymers wherein R to R are selected froin alkyl radicals having oneto four carbon atoms.

4. A stabilized polyacetal according to claim 3 wherein R to R areselected from alkyl radicals having one to four carbon atoms.

5. A stabilized polyacetal according to claim 3 wherein saidN-vinyl-azetidinone polymer is poly-N-vinyl-4methylazetidinone.

6. A stabilized polyacetal according to claim 3 wherein saidN-vinyl-azetidinone polymer is poly-N-vinyl-4,4-dimethylazetidinone.

7. A stabilized polyacetal according to claim 3 wherein saidN-vinyl-azetidinone polymer is poly-N-vinyl3,4-dimethylazatidinone.

8. A stabilized polyacetal according to claim 3 wherein saidN-vinyl-azetidinone polymer is poly-N-vinyl-4-phenylazetidinone.

9. A stabilized polyacetal according to claim 3 wherein saidN-vinyl-azetidinone polymer is a copolymer of N-vinyl-4,4-dimethyl-azetidinone and N-vinyl-N-methyl-formamide.

10. A stabilized polyacetal according to claim 3 containing in additionto said N-vinyl-azetidinone polymer from 0.01 to l0 percent by weight ofa phenolic antioxidant.

2. A process according to claim 1 wherein a mixture of saidnitrogen-containing polymer with another antioxidant or light stabilizeror with a mixture of another antioxidant and light stabilizer isincorporated in said polyacetal.
 3. A thermoplastic, moldable polyacetalwhich is a macromolecular homopolymer or formaldehyde or its cyclicoligomers or a copolymer of trioxane and cyclic ethers or cyclicacetals, which copolymer contains oxalkylene groups with at least twoadjacent carbon atoms in the main polymer chain, said polyacetal havingincorporated therein as a a nitrogen containing polymer selected fromthe group consisting of (1) homopolymers of a N-vinyl-azetidinone of theformula
 4. A stabilized polyacetal according to claim 3 wherein R1 to R4are selected from alkyl radicals having one to four carbon atoms.
 5. Astabilized polyacetal according to claim 3 wherein saidN-vinyl-azetidinone polymer is poly-N-vinyl-4-methyl-azetidinone.
 6. Astabilized polyacetal according to claim 3 wherein saidN-vinyl-azetidinone polymer is poly-N-vinyl-4,4-dimethyl-azetidinone. 7.A stabilized polyacetal according to claim 3 wherein saidN-vinyl-azetidinone polymer is poly-N-vinyl3,4-dimethyl-azatidinone. 8.A stabilized polyacetal according to claim 3 wherein saidN-vinyl-azetidinone polymer is poly-N-vinyl-4-phenyl-azetidinone.
 9. Astabilized polyacetal according to claim 3 wherein saidN-vinyl-azetidinone polymer is a copolymer ofN-vinyl-4,4-dimethyl-azetidinone and N-vinyl-N-methyl-formamide.
 10. Astabilized polyacetal according to claim 3 containing in addition tosaid N-vinyl-azetidinone polymer from 0.01 to 10 percent by weight of aphenolic antioxidant.